Relationship between the states of spinal impact injuries and magnetically evoked EMGs in rats

The relationship between the states of spinal impact injuries and magnetically evoked electromyograms (EMGs) were studied in rats. Impact injuries to the spinal cord were induced at a depth of 0.25-2.0 mm by insertion of a cylinder tip measuring 2 mm in diameter into the lumbar vertebrae L1-L2. Magnetically induced electromyograms for the brain and lumbar vertebrae L4-L5 were recorded from the tibialis anticus and the gastrocnemius muscles. H-reflex was not induced by the spinal cord injury (SCI) at a depth of 0.25 mm, although motor evoked potential (MEP) was observed. Continuous waves following the M-response were observed in the SCI at a depth of 0.25 mm. Elevation of the threshold, reduction of its latency and decrease in amplitude of the M-responses were observed at an injury depth of 0.5 mm or deeper. With SCI magnitude from mild (0.5 mm depth) to severe (1.0 mm depth), the amplitudes of the M-response were decreased, and the latency of the M-response was shorter than that of the control. The F-response was accelerated in severe SCI. Our results indicated that there was a relationship between extensive injury legions and the H-reflex F- and M-responses in magnetically evoked EMGs. Magnetically evoked EMGs are useful for monitoring the states of SCI.